Which of the following qualities do china and india have in common? a. mandarin is the most commonly spoken language. b. literacy rates are over 90% for all citizens. c. hinduism is the most commonly practiced religion. d. populations are over one billion.

The populations of both India and China are over one million. This is the quality that is similar between India and China.So the correct option in regards to the given question is option "D". China has the highest population in the world while India has the second highest population in the world. It can be surely mentioned that the literacy rate of India is not over 90% and so option "B" can be easily negated. Mandarin is also not a language that is commonly spoken in India and so option "A" can also be ruled out.

The answer is    d.  central highlands